The present invention relates to a method for manufacturing a semiconductor device, including a heat treatment method for activating impurity ion, which has been implanted into a semiconductor layer.
In recent years, there is an ever increasing demand for manufacturing processes for LSIs including MOS transistors in which the MOS transistors are miniaturized in order to further increase the speed and the degree of integration of LSIs.
In order to make advancements in the miniaturization of MOS transistors, it is necessary not only to reduce the gate length and the gate width of a transistor but also to reduce the height of the gate electrode and to realize shallower junctions by shallowing the junction plane of a source/drain diffusion layer.
Typically, a gate electrode of a MOS transistor is produced by forming a gate insulating film on a semiconductor substrate made of silicon, depositing a semiconductor layer made of polysilicon or amorphous silicon on the gate insulating film, and implanting impurity ion into the deposited semiconductor layer by an ion implantation method, so as to obtain an intended conductivity. Moreover, the source/drain diffusion layer is also formed by implanting impurity ion into the semiconductor substrate.
Herein, if the height of the gate electrode, i.e., the thickness of the deposited polysilicon film or amorphous silicon film, is reduced, it is necessary to also reduce the acceleration energy in the ion implantation when introducing an impurity. Similarly, it is necessary to reduce the acceleration energy in the ion implantation also for realizing a shallower junction of the source/drain diffusion layer.
On the other hand, in order to activate the impurity ion implanted into the semiconductor layer so as to provide a sufficient conductivity to the semiconductor layer despite the reduction in the acceleration energy, it is necessary to perform an annealing process for activating the impurity ion.
In the prior art, impurity ion is implanted into a semiconductor layer made of polycrystalline or amorphous silicon, and the implanted impurity ion is activated by performing an activation annealing process at a temperature of 700xc2x0 C. or more with the semiconductor layer being exposed, or by performing an activation annealing process at a temperature of 700xc2x0 C. or more after depositing a protection insulating film (cap layer) for an outward diffusion protection at a temperature of 700xc2x0 C. or more on the semiconductor layer.
A method for manufacturing a semiconductor device according to the first conventional example will now be described with reference to the drawings with respect to the activation annealing step for activating impurity ion, which has been implanted into a semiconductor layer.
FIG. 13(a) to FIG. 13(c) are cross-sectional views sequentially illustrating an impurity ion implantation step and an impurity ion activation annealing step according to the first conventional example.
First, as illustrated in FIG. 13(a), a semiconductor layer 102 made of amorphous silicon having a thickness of about 80 nm is deposited on an insulating film 101.
Then, as illustrated in FIG. 13(b), boron (B+) ion, for example, is implanted under implantation conditions including an acceleration energy of about 3 keV and an implantation dose of about 5xc3x971015 cmxe2x88x922, thereby forming an ion implantation region 102a in an upper portion of the semiconductor layer 102.
Then, as illustrated in FIG. 13(c), the semiconductor layer 102, into which boron ion has been implanted, is subjected to an activation annealing process in a nitrogen atmosphere at a temperature of about 900xc2x0 C. for about 30 minutes. Thus, the boron ion in the ion implantation region 102a is activated in the semiconductor layer 102, and diffuses through thermal diffusion to the vicinity of the interface with the insulating film 101.
By the activation annealing process, a portion of the implanted boron ion comes out of the semiconductor layer 102 through outward diffusion, and the semiconductor layer 102 is polycrystallized into a polysilicon layer 102B.
In order to reduce the outward diffusion, a nitrogen atmosphere containing oxygen (O2) is used in some cases as the annealing atmosphere. However, even if oxygen is contained in the annealing atmosphere, the outward diffusion cannot be suppressed completely, and the thickness of the polysilicon layer 102B is reduced because a surface portion of the semiconductor layer 102 is oxidized at the same time.
The second conventional example will now be described with reference to the drawings.
FIG. 14(a) to FIG. 14(d) are cross-sectional views sequentially illustrating a heat treatment process for activating impurity ion according to the second conventional example.
First, as illustrated in FIG. 14(a), a semiconductor layer 102 made of amorphous silicon having a thickness of about 80 nm is deposited on an insulating film 101.
Then, as illustrated in FIG. 14(b), boron (B+) ion, for example, is implanted under implantation conditions including an acceleration energy of about 3 keV and an implantation dose of about 5xc3x971015 cmxe2x88x922, thereby forming an ion implantation region 102a in an upper portion of the semiconductor layer 102.
Then, as illustrated in FIG. 14(c), a silicon oxide (SiO2) film 104 as a protection insulating film is deposited on the semiconductor layer 102 by using a CVD method. Since the deposition temperature of the silicon oxide film 104 is typically 600xc2x0 C. or more, a surface oxide film 103 is formed in a surface portion of the semiconductor layer 102 while the outward diffusion of boron ion also occurs. Furthermore, the semiconductor layer 102 is polycrystallized into a polysilicon layer 102A.
Now, a silicon oxide film obtained by using a CVD method, which is typically used in a transistor formation process (front end process) for LSIs, will be described.
First, a TEOS film is a silicon oxide film whose reaction temperature is about 650xc2x0 C. to 750xc2x0 C. and which is obtained through thermal decomposition of tetraethylorthosilicate (TEOS: Si(OC2H5)4). During the deposition, an oxygen gas is added to a TEOS gas.
Next, an HTO film is a silicon oxide film whose reaction temperature is about 700xc2x0 C. to 900xc2x0 C. and which is obtained through a thermal reaction of dinitrogen monoxide (N2O) with monosilane (SiH4) or dichlorosilane (SiH2Cl2).
Incidentally, the silicon oxide film 104 illustrated in FIG. 14(c) is an HTO film.
Then, as illustrated in FIG. 14(d), the semiconductor layer 102, into which boron ion has been implanted, is subjected to an activation annealing process in a nitrogen atmosphere at a temperature of about 900xc2x0 C. for about 30 minutes. Thus, the boron ion is activated in the polysilicon layer 102A, and diffuses through thermal diffusion to the vicinity of the interface with the insulating film 101 to form a polysilicon layer 102B.
As described above, with the first conventional example, it is not possible to obtain a predetermined impurity profile due to the occurrence of outward diffusion. Moreover, when an oxygen gas is added to the nitrogen atmosphere in order to suppress the outward diffusion, the semiconductor layer 102 is oxidized, thereby failing to obtain an intended thickness.
Moreover, with the second conventional example, the outward diffusion occurs during the deposition of the silicon oxide film 104, and the semiconductor layer 102 is exposed to an oxygen-containing gas in an early stage of the deposition, whereby the surface thereof is oxidized to form the surface oxide film 103. This is because of the following reason. When the silicon oxide film 104 is deposited at a temperature of 500xc2x0 C. or more, the semiconductor layer 102 is recrystallized (turned into polysilicon) to form the polysilicon layer 102A, and a large number of crystal grain boundaries occur in the polysilicon layer 102A, whereby the outward diffusion of impurity ion is likely to occur between these crystal grain boundaries.
Particularly, it is required to reduce the acceleration energy for the impurity implantation in order to reduce the height of the gate electrode and to shallow the source/drain diffusion layer so as to miniaturize MOS transistors. Therefore, the outward diffusion is more likely to occur, and the influence of the surface oxide film 103 on the operating characteristics of transistors is increased.
Moreover, in a case where a silicide film made of a high melting point metal such as tungsten silicide (WSi2) or a high melting point metal film such as tungsten (W) is provided in a MOS transistor, the silicide layer or the high melting point metal layer is oxidized (abnormally oxidized) during the activation annealing process containing an oxygen gas and during the deposition of a TEOS film or an HTO film by using a CVD method.
The present invention has been made to solve the problems in the prior art, and has an object to make it possible to suppress the outward diffusion of an implanted impurity from a semiconductor layer and a surface oxidization of the semiconductor layer during the process of activating the impurity, which has been implanted into the semiconductor layer.
In order to achieve the object, the present invention provides a method for manufacturing a semiconductor device, in which an insulating film to be a cap layer is formed at a low temperature of about 500xc2x0 C. or less on a semiconductor layer, into which impurity ion has been implanted, and an activation annealing process for activating the impurity ion is performed at a temperature of about 700xc2x0 C. or more and in a non-oxidizing atmosphere.
Specifically, a first method for manufacturing a semiconductor device of the present invention includes: a first step of implanting impurity ion into a semiconductor layer so as to form an ion implantation region in the semiconductor layer, and turning at least the ion implantation region amorphous; a second step of forming an insulating film on the semiconductor layer at a temperature at which the ion implantation region is not crystallized; and a third step of, after the second step, annealing the semiconductor layer in a non-oxidizing atmosphere so as to activate the impurity ion implanted into the semiconductor layer.
According to the first method for manufacturing a semiconductor device, at least an ion implantation region in a semiconductor layer is turned amorphous, and an insulating film is formed on the semiconductor layer at a temperature at which the ion implantation region is not crystallized, whereby the outward diffusion can be suppressed by the insulating film covering the semiconductor layer. In addition, since the insulating film is deposited at a temperature at which the ion implantation region is not crystallized, it is possible to also prevent the formation of a surface oxide film on the semiconductor layer in an early stage of the deposition. Moreover, even in a case where a metal silicide film or a high melting point metal film is formed on the semiconductor layer, for example, the metal silicide film or the high melting point metal film is not abnormally oxidized during the formation of the insulating film.
In the first method for manufacturing a semiconductor device, it is preferred that the semiconductor layer is deposited in an amorphous state in the first step, after which the impurity ion is implanted. This corresponds to, for example, a case where a semiconductor layer is formed in an amorphous state as a gate electrode forming layer. When an insulating film is formed on an amorphous semiconductor layer at a temperature of about 500xc2x0 C. or less, the semiconductor layer is not recrystallized, whereby it is possible to prevent the outward diffusion occurring due to crystal grain boundaries.
Moreover, in the first method for manufacturing a semiconductor device, it is preferred that the semiconductor layer is deposited in a polycrystalline state in the first step, after which the impurity ion is implanted into the deposited semiconductor layer, thereby turning the ion implantation region amorphous. This corresponds to, for example, a case where a semiconductor layer is formed as an impurity diffusion layer such as a source/drain. Even in a case where the semiconductor layer is a single crystal layer, an ion implantation region of the semiconductor layer is turned amorphous if it is implanted at a relatively high dose. Therefore, an insulating film is formed on the ion implantation region, which has been turned amorphous, in the semiconductor layer at a temperature at which the ion implantation region is not crystallized, whereby the ion implantation region is not recrystallized, and thus it is possible to prevent the outward diffusion occurring due to crystal grain boundaries.
A second method for manufacturing a semiconductor device of the present invention includes: a first step of forming a gate insulating film on a semiconductor substrate; a second step of forming a semiconductor layer made of amorphous silicon or polycrystalline silicon on the gate insulating film; a third step of implanting impurity ion into a gate electrode forming region of the semiconductor layer so as to form an ion implantation region in the gate electrode forming region; a fourth step of, after the third step, forming an insulating film on the semiconductor layer at a temperature at which the ion implantation region is not crystallized; a fifth step of, after the fourth step, annealing the semiconductor layer in a non-oxidizing atmosphere so as to activate the impurity ion; and a sixth step of, after the fifth step, patterning the gate electrode forming region of the semiconductor layer so as to form a gate electrode from the semiconductor layer.
The second method for manufacturing a semiconductor device is a method for forming a gate electrode in a MIS transistor, in which an ion implantation region, into which impurity ion is implanted, is formed in a gate electrode forming region of a semiconductor layer made of amorphous silicon or polycrystalline silicon, after which an insulating film is formed on the ion-implanted semiconductor layer at a temperature at which the ion implantation region is not crystallized, and then the semiconductor layer is annealed in a non-oxidizing atmosphere. Therefore, as in the first method for manufacturing a semiconductor device of the present invention, it is possible to suppress the outward diffusion of impurity ion from the semiconductor layer and the formation of a surface oxide film on the semiconductor layer.
In the first or second method for manufacturing a semiconductor device, it is preferred that: the temperature at which the semiconductor layer is not crystallized is a temperature of 500xc2x0 C. or less; and a temperature of the annealing is 700xc2x0 C. or more.
A third method for manufacturing a semiconductor device of the present invention includes: a first step of sequentially forming a gate insulating film and a gate electrode on a semiconductor substrate made of silicon; a second step of implanting impurity ion onto the semiconductor substrate using the gate electrode as a mask so as to form an amorphous ion implantation region in the semiconductor substrate; a third step of forming an insulating film across an entire upper surface of the semiconductor substrate including the gate electrode at a temperature at which the ion implantation region is not crystallized; and a fourth step of, after the third step, annealing the semiconductor substrate in a non-oxidizing atmosphere so as to activate the impurity ion, thereby forming an impurity diffusion layer in a region of the semiconductor substrate beside the gate electrode.
The third method for manufacturing a semiconductor device is a method for forming an impurity diffusion layer in a MIS transistor, in which impurity ion is implanted onto a semiconductor substrate using a gate electrode as a mask so as to form an ion implantation region in the semiconductor substrate, after which an insulating film is formed across the entire upper surface of the ion-implanted semiconductor substrate including the gate electrode at a temperature at which the ion implantation region is not crystallized, and then the semiconductor substrate is annealed in a non-oxidizing atmosphere. Therefore, as in the first method for manufacturing a semiconductor device of the present invention, it is possible to suppress the outward diffusion of impurity ion from the impurity diffusion layer and the formation of a surface oxide film on the impurity diffusion layer. Moreover, in a case where the gate electrode is made of polysilicon into which impurity ion is implanted, it is possible to also suppress the outward diffusion of impurity ion from the gate electrode and the surface oxidization of the gate electrode.
It is preferred that the third method for manufacturing a semiconductor device further includes, after the fourth step, a fifth step of anisotropically etching the insulating film so as to form a side wall, which is made of the insulating film, on a side surface of the gate electrode.
In this way, the side wall of the gate electrode can be formed from the insulating film for preventing outward diffusion during the activation annealing process, whereby it is possible to simplify the manufacturing process. In addition, when impurity ion is implanted again using the formed side wall and the gate electrode as a mask, the initial impurity diffusion layer can made to function as an LDD diffusion layer, an extension diffusion layer or a pocket diffusion layer.
In this case, it is preferred that method for manufacturing a third semiconductor device further includes, after the fifth step: a sixth step of depositing a metal film across an entire upper surface of the semiconductor substrate including the gate electrode; and a seventh step of subjecting the deposited metal film to a heat treatment so as to form a metal silicide film along an interface between the metal film and the gate electrode and an interface between the metal film and the impurity diffusion layer.
In this way, an upper portion of the gate electrode or the impurity diffusion layer is silicified, whereby it is possible to reduce the resistance of the gate electrode or the contact resistance of the impurity diffusion layer.
In this case, it is preferred that the metal silicide film is made of tungsten silicide, molybdenum silicide, titanium silicide, cobalt silicide or nickel silicide.
In the third method for manufacturing a semiconductor device, it is preferred that the first step includes a step of forming a metal film or a metal silicide film on the gate electrode.
In this way, the gate electrode is in a polymetal electrode structure having a metal film in an upper portion thereof or a polycide electrode structure having a metal silicide film in an upper portion thereof. In addition, since the insulating film is formed at a temperature of about 500xc2x0 C. or less, the metal film or the metal silicide film is not substantially oxidized.
In this case, it is preferred that: the metal film is made of tungsten; and the metal silicide film is made of tungsten silicide, molybdenum silicide, titanium silicide, cobalt silicide or nickel silicide.
A fourth method for manufacturing a semiconductor device of the present invention includes: a first step of sequentially forming a gate insulating film and a gate electrode containing silicon on a semiconductor substrate made of silicon and having a first region and a second region; a second step of implanting impurity ion onto the semiconductor substrate using the gate electrode as a mask so as to form an ion implantation region in the semiconductor substrate and turning the ion implantation region amorphous; a third step of forming an insulating film across an entire upper surface of the semiconductor substrate including the gate electrode at a temperature at which the ion implantation region is not crystallized; a fourth step of, after the third step, annealing the semiconductor substrate in a non-oxidizing atmosphere so as to activate the impurity ion, thereby forming an impurity diffusion layer in a region of the semiconductor substrate beside the gate electrode; a fifth step of, after the fourth step, removing a portion of the insulating film that is included in the first region and that is above the gate electrode or the impurity diffusion layer; and a sixth step of, after the fifth step, depositing a metal film across an entire upper surface in the first region and the second region and subjecting the deposited metal film to a heat treatment so as to form a metal silicide film along an interface between the metal film and the gate electrode and an interface between the metal film and the impurity diffusion layer in the first region.
According to the fourth method for manufacturing a semiconductor device, an insulating film is formed on a semiconductor substrate, into which impurity ion has been implanted to form an ion implantation region, at a temperature at which the ion implantation region is not crystallized in the third step, and annealing is performed in a non-oxidizing atmosphere so as to activate the impurity ion in the semiconductor substrate in the fourth step. In this way, effects as those of the first method for manufacturing a semiconductor device of the present invention can be obtained. In addition, a portion of the insulating film that is included in the first region and that is above the gate electrode or the impurity diffusion layer is removed in the fifth step, thereby leaving the insulating film included in the second region. Therefore, when preventing the silicification of the gate electrode and the impurity diffusion layer in the second region, it is no longer necessary to separately form a mask film for preventing silicification, whereby it is possible to simplify the manufacturing process.
In the third or fourth method for manufacturing a semiconductor device, it is preferred that: the temperature at which the semiconductor substrate is not crystallized is a temperature of 500xc2x0 C. or less; and a temperature of the annealing is 700xc2x0 C. or more.
In the first to fourth methods for manufacturing a semiconductor device, it is preferred that the insulating film is a silicon oxide film obtained by reacting tetraethylorthosilicate (TEOS) and ozone with each other. In this way, it is possible to reliably form an insulating film made of silicon oxide at a reaction temperature of about 500xc2x0 C. or less.
In the first to fourth methods for manufacturing a semiconductor device, it is preferred that: the annealing is performed by a rapid thermal annealing (RTA) method or a furnace annealing (FA) method; and the non-oxidizing atmosphere is made of nitrogen or argon.